st: RE: Panel Data Manipulation

1.
gen byte sold = volume > 0 & volume < .
bysort sold seller buyer (year) : gen firstyear = year[1] if sold
bysort seller buyer (firstyear) : replace firstyear = firstyear[1]
2.
I did one; now you do one.
Nick
n.j.cox@durham.ac.uk
Jason Hwang
> I would appreciate help with the following panel data manipulation
> problem. I have data of the form:
>
> seller year product buyer volume
> ...
> 100 1990 1111 200 100
> 100 1991 1111 200 200
> 100 1992 1111 200 250
> 100 1990 2222 200 .
> 100 1991 2222 200 80
> 100 1992 2222 200 83
> 100 1990 2222 500 100
> 100 1991 2222 500 125
> 100 1992 2222 500 200
> ...
>
> The dot in volume means sales volume in that year was zero. I
> would like
> summarize the data by answering two questions. First, each
> seller sells
> many products to many buyers. Let "firstyear" be the first
> year a given
> seller sells anything to a given buyer. In the example above, for the
> seller-buyer pair 100-200, "firstyear" would be 1990. Then
> for every other
> product 100 sells to 200 in subsequent year, I want to
> calculate the gap
> between year of first sale and "firstyear". I would like to generate a
> table of the form:
>
> seller product buyer timegap firstyear
> ...
> 100 1111 200 0 1990
> 100 2222 200 1 1991
> 100 2222 300 0 1990
> ...
>
> Second, I would like to ask: for each seller, how much of the
> increase in
> total sales of each product is driven by changes in sales to existing
> buyers or sales to new buyers. I would like to generate a table of the
> form:
>
> seller product year change same new
> ...
> 100 1111 1991 100 100 0
> 100 2222 1991 105 25 80
> ...
>
> Note that from 1990 to 1991, the total sales of 2222
> increased by 105, of
> which 25 came from increasing sales to an existing customer
> 500, and the
> rest 80 came from selling to a new customer 200.
>
> One complication is that sometimes a seller will make sales
> with a given
> buyer in one year, make zero sales the next year, and
> generate positive
> sales another year. In the case of this last year, I would
> like to count
> the sales as coming from "same" customer.
>
> I would very much appreciate your help. Thanks very much.
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